1. Technical Field
The present invention relates to an ink composition, an ink set, and an image forming method.
2. Description of the Related Art
In recent years, as a result of ever-increasing demand for the protection of resources, the protection of the environment, the enhancement of operational stability, and the like, the conversion of paints and inks into aqueous products is advancing. As in the case of oil-based paints and oil-based inks, the qualities required in aqueous paints and aqueous inks include fluidity, storage stability, glossiness of film, clarity, coloring ability, and the like. However, compared to oil-based vehicles, most pigments have a markedly poor adaptability to aqueous vehicles with respect to pigment dispersibility and the like and, therefore, satisfactory quality cannot be obtained by conventional dispersion methods. The use of various additives, for example, aqueous pigment dispersion resins or surfactants, has hitherto been studied, but an aqueous paint or an aqueous ink that satisfies all the adaptation properties described above and is comparable to existing high quality oil-based paints or high quality oil-based inks has not been obtained.
In order to solve these problems, for example, an aqueous pigment ink containing a pigment dispersion containing pigment particles that are encapsulated by a polymer containing 20% by mass to 70% by mass of aromatic rings has been disclosed (see, for example, U.S. Patent Application Publication No. 2005/0124726). Further, a pigment ink for ink-jet recording containing a pigment dispersion which is prepared by using, as a dispersant, a random copolymer of a hydrophilic monomer and a hydrophobic monomer, in which the content of the hydrophobic monomer is 50% by weight to 80% by weight with respect to the polymer weight, has been disclosed (see, for example, U.S. Patent Application Publication No. 2006/0014855).
In addition, a technique for obtaining ink-jet output materials having excellent cured film strength by using a pigment dispersion which is prepared by using a polymerizable group-introduced dispersant and a UV curing type material in combination has been disclosed (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2004-97955).